sin（α+β）=sinαcosβ+cosαsinβ
sin（α-β）=sinαcosβ-cosαsinβ
cos(a+b)=cosacosb-sinasinb
cos(a-b)=cosacosb+sinasinb
sh(x±y)=shxchy±chxshy
ch(x±y)=chxchy±shxshy